1. Field of the Invention
The present invention relates to an ionizer and static charge eliminating method for eliminating static charge in a static charge elimination region.
2. Description of the Related Art
Heretofore, ionizers, which utilize corona discharge, have been known as one type of static charge eliminating apparatus for eliminating static electricity within a static charge elimination region (e.g., on a body charged with static electricity). See, for example, U.S. Pat. No. 6,693,788, Japanese Laid-Open Patent Publication No. 2008-288072, and International Publication No. WO2007/122742. Such ionizers release to the static charge elimination region positive ions or negative ions, which are generated by corona discharge caused by application of high voltage to electrodes, whereupon the static electricity contained within the static charge elimination region is eliminated by the positive ions or the negative ions.
An explanation shall now be made with reference to FIGS. 8A through 12B concerning the ionizers disclosed in U.S. Pat. No. 6,693,788, Japanese Laid-Open Patent Publication No. 2008-288072, and International Publication No. WO2007/122742. For facilitating such explanations, in FIGS. 8A through 12B, portions of the structural elements thereof are shown as exaggerated or schematic representations.
As shown in FIG. 8A, the ionizer according to the specification of U.S. Pat. No. 6,693,788 is equipped with a needle electrode 100, and ground electrodes 102, which are arranged between the body 104 from which static charge is to be eliminated and the needle electrode 100. In the case that, for example, an AC voltage having a period of T and a duty ratio of 50% (i.e., a high voltage in which an applied voltage of +V and an applied voltage of −V are repeated reciprocally) is applied to the needle electrode 100, a non-illustrated electric field (lines of electric force) is formed between the needle electrode 100 and the ground electrodes 102 that confront the needle electrode 100. Owing thereto, an electric field concentration is generated at the tip end of the needle electrode 100, and by means of corona discharge that is caused by the electric field concentration, in the positive half-period of the AC voltage (+V applied voltage), positive ions 106 are generated in the vicinity of the tip portion (see FIG. 9A), whereas, in the negative half-period of the AC voltage (−V applied voltage), negative ions 108 are generated in the vicinity of the tip portion (see FIG. 9B).
Accordingly, by passing the positive ions 106 or the negative ions 108 between the two ground electrodes 102 (i.e., through an opening provided in the ionizer) and releasing such ions toward the body 104, the electric charge (static electricity), which has charged the body 104, is eliminated.
Further, as shown in FIG. 8B, the AC voltage is switched between positive and negative polarities at a timing indicated by times t50, t51, t52, t53, t54, t55.
As shown in FIG. 10, in the ionizer disclosed in Japanese Laid-Open Patent Publication No. 2008-288072, when ionization is observed from the body 104, two needle electrodes 100a, 100b are arranged between two ground electrodes 102. In this case, when a +V direct current voltage is applied to one of the needle electrodes 100a and a −V direct current voltage is applied to the other of the needle electrodes 100b, the electric fields are added to the region between the needle electrode 100a and the ground electrode 102, as well as between the needle electrode 100b and the ground electrode 102, and a non-illustrated electric field (lines of electric force) is formed between the needle electrode 100a and the needle electrode 100b. As a result, positive ions 106 are generated in large quantities in the vicinity of the tip end of the needle electrode 100a, whereas negative ions 108 are generated in large quantities in the vicinity of the tip end of the needle electrode 100b, due to the corona discharge caused by the electric field concentrations generated at the tip ends of the needle electrodes 100a, 100b. The positive ions 106 and the negative ions 108 pass through openings between each of the ground electrodes 102 and are released respectively toward the body 104, whereupon static electricity of the body 104 is eliminated.
As shown in FIG. 11A, International Publication No. WO2007/122742 discloses a structure in which ground electrodes 102 (refer to FIG. 8A and FIGS. 9A though 10) are not necessary. In this case, an AC voltage as shown in FIG. 11B is applied to one of the needle electrodes 100a, and an AC voltage as shown in FIG. 11C, which is 180° opposite in phase with respect to the aforementioned AC voltage, is applied to the other of the needle electrodes 100b. Further, as shown in FIGS. 11B and 11C, the respective AC voltages are switched between positive and negative polarities at a timing indicated by times t60, t61, t62, t63, t64, t65.
As a result thereof, for example, as shown in FIG. 12A, when an applied voltage of +V (see FIG. 11B) is applied to the needle electrode 100a and an applied voltage of −V (see FIG. 11C) is applied to the needle electrode 100b, non-illustrated electric fields (lines of electric force) are formed between each of the needle electrodes 100a, 100b, and large electric field concentrations are generated at each of the tip ends of the needle electrodes 100a, 100b. By means of corona discharge that is caused by the electric field concentrations, positive ions 106 are generated in large quantities in the vicinity of the tip portion of the needle electrode 100a, whereas negative ions 108 are generated in large quantities in the vicinity of the tip portion of the needle electrode 100b. The positive ions 106 migrate toward the needle electrode 100b along the lines of electric force, and the negative ions 108 migrate toward the needle electrode 100a along the lines of electric force.
Additionally, at a switchover timing between positive and negative polarities at times t61, t63, t65, when the voltage level of the needle electrodes 100a, 100b becomes zero, as shown in FIG. 12B, the positive ions 106 and the negative ions 108 between the needle electrodes 100a, 100b are released toward the body 104, whereupon static electricity is eliminated from the body 104. Further, in FIGS. 12A and 12B, groupings of positive ions 106 or negative ions 108 are shown by the broken line regions that surround the positive ions 106 or the negative ions 108.
However, with the ionizer according to the specification of U.S. Pat. No. 6,693,788, as shown in FIGS. 9A and 9B, because positive ions 106 and negative ions 108 are induced and absorbed by the ground electrodes 102 along the non-illustrated lines of electric force, which are formed between the needle electrode 100 and the ground electrodes 102, the number of positive ions 106 or negative ions 108 that actually reach the body 104 is reduced.
On the other hand, the ionizer of Japanese Laid-Open Patent Publication No. 2008-288072 shown in FIG. 10 is capable of generating positive ions 106 or negative ions 108 in large quantities, because the electric field concentration at the tip ends of the needle electrodes 100a, 100b is large compared to the ionizer disclosed in the specification of U.S. Pat. No. 6,693,788 (see FIGS. 8A to 9B). Notwithstanding, similar to the case of U.S. Pat. No. 6,693,788, positive ions 106 and negative ions 108 tend to be induced and absorbed respectively by the ground electrodes 102. Further, the positive ions 106 migrate toward the needle electrode 100b, whereas the negative ions 108 migrate toward the needle electrode 100a. Owing thereto, the positive ions 106 and the negative ions 108 join together during migration thereof, and the negative ions 108 are induced and absorbed by the needle electrode 100a, and in addition, the positive ions 106 are induced and absorbed by the needle electrode 100b. As a result, even though positive ions 106 and negative ions 108 are generated in large quantities, the number of positive ions and negative ions required to eliminate static electricity from the body 104 cannot be increased. Consequently, with the ionizer of Japanese Laid-Open Patent Publication No. 2008-288072, large quantities of ions are generated uselessly.
With respect to this problem, with the ionizer of International Publication No. WO2007/122742 shown in FIGS. 11A to 12B, since the ground electrodes 102 (see FIG. 8A and FIGS. 9A to 10) are made unnecessary, induction and absorption of the positive ions 106 and the negative ions 108 by such ground electrodes 102 can be avoided. However, in the case that switching is carried out between positive and negative portions of the AC voltage at the timing of times t60, t61, t62, t63, t64, t65, because the polarity of the AC voltage applied to the needle electrodes 100a, 100b is switched immediately after the positive ions 106 and the negative ions 108 are directed and released toward the body 104, the positive ions 106 and the negative ions 108 that are directed toward the body merge together, whereupon the positive ions 106 and the negative ions 108 are induced and absorbed by the needle electrodes 100a, 100b immediately after switching in polarity. As a result, the number of positive ions 106 and negative ions 108 that are released toward the body 104 is reduced.
In this manner, with the ionizers disclosed in U.S. Pat. No. 6,693,788, Japanese Laid-Open Patent Publication No. 2008-288072, and International Publication No. WO2007/122742, the generation efficiency of ions (release rate of ions from the ionizer) needed to eliminate static electricity from the body is reduced, and consequently, the efficiency at which static electricity is eliminated by such ionizers is low.
With respect to the aforementioned problems, it can be considered to arrange the ground electrodes rearwardly of the needle electrodes 100, 100a, 100b and to increase the electric field concentration at the tip ends of the needle electrodes 100, 100a, 100b, or alternatively, to raise the voltage level of the needle electrodes 100, 100a, 100b. However, in the event that the ground electrodes are positioned rearwardly of the needle electrodes 100, 100a, 100b, because it is necessary to secure space for arrangement of the ground electrodes, the ionizer is made larger in scale. On the other hand, in the case that the voltage level is raised to cause generation of ions in large quantities, due to the above-described problems with U.S. Pat. No. 6,693,788, Japanese Laid-Open Patent Publication No. 2008-288072, and International Publication No. WO2007/122742, static electricity elimination efficiency cannot be increased. Further, because in order to raise the voltage level, a high voltage generator for generating higher voltage is needed, in this case as well, the ionizer is made larger in scale.